This invention relates to a plastic movable guide for an endless, flexible, circulating power transmission medium, such as a chain in a chain and sprocket transmission, or a belt in a belt and pulley transmission.
Many machines, such as automobile engines, include a transmission device, which transmits power by means of a chain, a belt or the like. A movable guide is maintained in sliding contact with the transmission medium, and cooperates with a tensioner to maintain tension and to prevent vibration of the medium in its plane of travel and also to prevent transverse vibration. A movable guide is typically pivotally mounted on the frame of the engine or other machine by a shaft such as a bolt or a pin.
FIGS. 8 and 9 show a plastic movable guide 300 used as a tensioner lever in a chain transmission disclosed in Japanese Patent Application No. 2000-382798. This plastic movable guide 300 comprises a guide body 301, including an elongated shoe 302 having a front surface for sliding contact with a traveling chain, belt or the like, and a plate-receiving portion 303 extending longitudinally on the back of he shoe 302. The shoe and plate-receiving portion are integrally molded as a unit from a synthetic resin. A reinforcing plate 308, made of a rigid material, for reinforcing the guide body 301, fits into a longitudinally extending slot 307, which opens at the edge of the plate-receiving portion 303, the opening facing in a direction opposite to the direction in which the front surface of the shoe faces. At one end of the plate-receiving portion 303, a mounting hole 305 is provided for mounting the guide body on the frame of an engine or other machine. A through hole 308A is provided at one end of the reinforcing plate 308. When the reinforcing plate and guide body are assembled together with the reinforcing plate fitting into slot 307, the through hole 308A and the mounting hole 305 are in register with each other, and receive a mounting bolt, pin or the like.
Because the plate-receiving portion 303 and the shoe 302 are integrally molded of synthetic resin, the guide body itself presents a surface for sliding contact with the flexible transmission medium, and it not necessary to provide a separate shoe. Consequently, the number of parts, and the number of steps needed to fabricate the guide, are reduced. Since a longitudinal slot 307, opening at the edge of the plate-receiving portion 303 receives a reinforcing plate 308, the rigidity, toughness, strength of the plastic movable guide, and especially the rigidity of the guide against bending in the plane of pivoting movement, are significantly improved.
In the conventional plastic movable guide 300, the relationships between the respective sizes and shapes of the guide body 301 and the reinforcing plate 308 have not been considered important, and, in practice, the size and shape of the reinforcing plate 308 have been designed to be the same as the size and shape of the slot in the guide body 301. However, variations in production accuracy and differences between coefficients of thermal expansion of materials cause the end of the reinforcing plate to protrude slightly from the guide body.
The above-described plastic movable guide produces more noise than a plastic movable guide composed only of resin material.
A reinforcing plate made of a rigid material such as metal wears more readily than the resin forming the guide body. Thus, it is necessary to subject the reinforcing plate to a preliminary strengthening process such as heat treatment to enhance its wear resistance. The preliminary treatment of the reinforcing plate increases the production cost of the guide. The preliminary treatment also causes distortion of the reinforcing plate, resulting in difficulties in fitting the reinforcing plate into the slot of the guide body.
The inventors have studied and analyzed the cause of noise in plastic movable guides, and the cause of wear of the reinforcing plate, and have found unexpectedly that the above-mentioned problems do not occur in all plastic movable guides, but only in guides in which an end of the reinforcing portion protrudes from the slot of the guide body. They found that direct contact between a plunger of the tensioner and the reinforcing plate causes the generation of noise in the conventional plastic movable guide, and also causes the reinforcing plate to wear earlier than the guide body.
Accordingly, among the objects of the invention are the solution of the above-mentioned problems of prior art plastic movable guides and the provision of a plastic movable guide having superior quietness of operation, easy assembly and reduced production cost.
The plastic movable guide in accordance with the invention comprises an elongated guide body and a reinforcing plate. The guide body is composed of an elongated shoe having a front surface for sliding contact with the power transmission medium and a back side, and a plate-receiving portion extending longitudinally along the back side of said shoe and having a longitudinally extending slot having an opening facing in a direction opposite to the direction in which the front surface of the shoe faces. The shoe and plate-receiving portion are integrally molded as a unit from a synthetic resin. The reinforcing plate fits into the slot, and the guide body and reinforcing plate are pivotable about a mounting located adjacent one end of the guide body. A part of the plate-receiving portion, remote from the pivoting end of the guide body, forms a plunger-engaging surface, engageable with the plunger of a tensioner. The plunger-engaging surface is divided by the opening of the slot, and the reinforcing plate is recessed in the slot, at least at the location at which the slot divides the plunger-engaging surface, so that the reinforcing plate does not protrude from the part of the opening of the slot that divides the plunger-engaging surface.
Preferably a mounting hole for mounting the guide is provided adjacent said one end of the guide body, and a through hole is provided adjacent an end of the reinforcing plate. These through holes are in register with each other when the reinforcing plate is located in said slot so that the reinforcing plate and the guide body may be held together by, and pivoted on, a shaft extending through the mounting holes.
The plastic material forming a guide body is not especially limited. However, since the sliding contact surface of the guide body functions as a shoe, the material is preferably a so-called xe2x80x9cengineering plastic,xe2x80x9d such as a polyamide resin, having excellent wear resistance and lubricating properties. A fiber-reinforced resin may be used either with or without a non-reinforced resin. The material of the reinforcing plate is not especially limited but should be selected so that the reinforcing plate has the bending rigidity and strength required for a plastic movable guide. Iron based metals, nonferrous metals such as aluminum, magnesium, titanium and the like, engineering plastics such as polyamide resin and the like, or fiber reinforced plastics are preferably used.
The following unique effects are obtained by a plastic movable guide having the above structure.
The plunger of the tensioner is engaged by a large area of the guide body, and therefore the contact area between the movable guide and the plunger is much greater than in the case where the plunger and the reinforcing plate directly contact each other. Accordingly the contact pressure is reduced, which results in decreased wear of the reinforcing plate at the location of the plunger-engaging portion of the guide body. Since the tensioner plunger engages only the plastic material of the guide body, no metallic noise is generated. Moreover, the plastic material of the guide body also absorbs vibrations better than in the case where the plunger and the reinforcing plate contact each other directly. Thus, the plastic movable guide in accordance with the invention pivots quietly, imparting appropriate tension to a chain, a belt or the like, and also reliably prevents vibration of the chain, belt or the like, including both vibrations in the plane of circulation, and transverse vibrations.
Because the guide body and reinforcing plate are held together by a mounting shaft that extends through mounting holes in both elements, the guide body and the reinforcing plate can pivot about the mounting shaft in cooperation with each other, without the reinforcing plate becoming disconnected from the guide body. Even if there is a difference between the coefficients of thermal expansion of the reinforcing plate and the guide body, the reinforcing plate and guide body are secured together at one end and are free to expand and retract longitudinally relative to each other so that deformation and breakage due to thermal effects are avoided.